Which of the eight D aldohexoses give the same aldaric acids as their L enantiomers?

Name: Problem 50, Chapter 21: Organic chemistry with biological applications
Uploaded: 2020-06-01T20:36:43-08:00
Duration: 6 min 56 s
Channel: Ricajoy Montero
Description: Which of the eight D aldohexoses give the same aldaric acids as their L enantiomers?

step 1 Okay, number 51, we're dealing with alderic acids. Okay, so the strategy that I would want to us

Which of the eight D aldohexoses give the same aldaric acids...

Key Concepts

Aldohexoses

Aldohexoses are six?carbon sugars that contain an aldehyde group at one end and several chiral centers along the carbon chain. Their stereochemical diversity (with eight possible isomers in the D series) underlies much of carbohydrate chemistry, as the spatial arrangement of the hydroxyl groups determines their chemical behavior and reactivity.

Enantiomers

Enantiomers are pairs of molecules that are non?superimposable mirror images of each other. In the context of sugars, the D and L forms are enantiomeric pairs, meaning they have exactly opposite configurations at every chiral center. Many chiral reactions produce products that are themselves chiral, but in some cases – such as when symmetry is introduced – the final product may become identical for both enantiomers.

Aldaric Acids

Aldaric acids are the dicarboxylic acids obtained by the oxidation of both the aldehyde and the terminal primary alcohol group in aldoses. When an aldohexose is fully oxidized, the two ends are converted into carboxyl groups while the stereochemistry at the internal four carbons is retained, leading to a six?carbon diacid whose chirality depends on the configuration of these middle centers.

Meso Compounds and Molecular Symmetry

A meso compound is one that contains stereocenters yet is overall achiral due to an internal plane of symmetry. In the oxidation of aldohexoses to aldaric acids, if the configuration of the four internal centers is symmetric – i.e. the sequence is palindromic – the resulting aldaric acid is meso. Thus, when a D sugar whose internal configuration is self?complementary is oxidized, it will give the same (achiral) product as its enantiomer, L.

Transcript

00:01 Okay, number 51, we're dealing with alderic acids.

00:04 Okay, so the strategy that i would want to use in this type of problem is to look for these sugars with a lot of symmetry.

00:16 Okay, so since we're converting to alderic acid, once you have that carboxylic acid, both on carbon 1 and carbon 6, if you have a lot of symmetry between carbons 2 and 4, then you're pretty much good to go.

00:34 Okay, so i'll show you what i mean as we go.

00:39 So i'll just start with the aloes.

00:43 Okay, so again, we're looking for a lot of symmetry.

00:48 And the aloes is pretty good for that.

00:52 So let me go ahead and draw it, s .h2.

00:54 Oh and we have four carbons in between and all the oh groups are on the right side.

01:04 Okay, all the oh groups are on the right side.

01:14 Right, so there's this symmetry, some kind of symmetry going on in this kind of plane.

01:24 Okay, so there's symmetry between the top part and the bottom part.

01:29 This is the only difference that we're seeing and again, once you'll convert this to an alderic acid, that difference is not going to be present anymore.

01:39 Okay, so this is actually your d allos.

01:44 Okay, so i'll go ahead and write that.

01:46 This is your d aloes.

01:49 And i'll just go ahead and draw the l aloes.

01:55 So we could see that mirror image.

02:00 So we have ch2oh.

02:04 And we're going to have all those oh groups on the left side...

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